Just how ancient? No one’s quite sure, but the rare, recently found fossils are 146 million to 157 million years old, give or take a few million years.

Although fossils have been discovered in all seven layers of rock formations visible at the monument, two of the three latest and quite rare finds were discovered within days of each other last month. All three fossils — rare turtle tracks, lizard tracks and a 7-inch, intact three-toed, dinosaur track — came from the Morrison formation, the topmost layer at the monument that is visible along Rim Rock Drive.

The discoveries were partly by chance, monument staff said.

In 2005, paleontologist John Foster discovered rare turtle tracks on the underbelly of a rock outcropping at the monument. That rock had slid down an embankment and was lying with the fossils face down.

On Sept. 16, monument maintenance worker Jim Roberson came across the intact fossil of a bipedal dinosaur. The fossil was not encased in stone, but lying along a sandy embankment.

After the dinosaur track discovery, the monument’s chief of interpretation, Michelle Wheatley, invited Foster to the monument on Sept. 22 to retrieve the rock that held the turtle impressions. On that day, while they were waiting for a truck to help haul the heavy rock, the two poked around the area where the dinosaur track had been located the week before.

They came across a rock with ripples, the bumps indicating they had been formed by water. When Foster picked up the rock it cracked, and the lizard tracks were found inside.

“He said, ‘Holy cow, do you see what I see?’ ” Wheatley recalled Foster saying. “It was just by pure chance that we found the lizard tracks when we were at the other site. That was a really fun day for us.”

Foster said he hasn’t determined whether the dinosaur track is from a carnivorous or plant-eating animal. He estimates it stood 10-feet tall. The lizard tracks are a type of track that never before has been found in the Morrison formation, he said. And the turtle tracks are considered to be rare, having only been found in one other area in North America.

Wheatley said there are a couple of theories about how the dinosaur track ended up there. It may have been part of rock that was thrust over the edge during the building of the 1930s-era road, Rim Rock Drive. At that time, rock and debris were sloughed off downhill to aid construction. Or, the dinosaur track could have been encased in a rock that was made of softer stone than the fossil. Over time, the rock surrounding the fossil gave way.

About 30 people showed at Colorado National Monument’s visitor center Wednesday to ogle the finds. The day also marked National Fossil Day.

Wes Allen of Grand Junction excitedly snapped multiple photos of the fossils as local paleontologists answered questions. An avid hiker, Allen said he tries to keep his eyes peeled for such finds.

“I could have walked across some of these exhibits while walking today,” he said.